Groups including the Wilderness Society and the Center for Biological Diversity said the plan allows too much off-road vehicle use, livestock grazing and oil and gas development on the 2.8 million acres of public lands.

The Arizona Strip stretches for miles north of the Grand Canyon National Park and includes the Vermilion Cliffs and Grand Canyon-Parashant national monuments.

There are no paved roads on either monument, but several graded gravel roads on the latter. "They mostly are primitive two-track roads that are very infrequently traveled," said Scott Florence, BLM district manager for the Arizona Strip.

Critics contended that the plan, which took effect Friday upon being published in the Federal Register, would not prevent habitat fragmentation for such key wildlife species found in the region as deer, elk and mountain lions.

It also would do little on behalf of the desert tortoise and other threatened, endangered and sensitive species, they said.

Wildlife habitat and archaeological sites will be sacrificed to oil and gas development, off-road vehicles and livestock grazing under the plan BLM issued, members of several environmental organizations said.

"Page after page, the BLM finds ways to promote continued off-road vehicle use in places that were set aside for their ancient artifacts, rugged landscapes, and habitat for desert species," said Nada Culver, Wilderness Society senior counsel.

The BLM's 3,000-page plan ignored why national monuments were created and disregards the wishes of the public to protect them, she said.

But federal officials defended the plan as the most practical, saying it allows people to use the land while protecting it. It has been debated for several years.

Florence said his agency was trying to be as proactive as possible and that the U.S. Fish and Wildlife Service issued a no-jeopardy biological opinion concerning the plan's impact on the desert tortoise.

"It isn't surprising that they would take that position because they did in their comments and protests on the final plan," he said.

"In developing the plans, we looked at the monument proclamations and feel that we developed plans that will adequately protect those monument objects while allowing for other uses out there.

"They seem to be focused a lot on the route designations, and in developing the plans we did close several hundred miles of routes to vehicle use."

Florence said a total of 290 miles of roads and trails on the two monuments would be closed under the plan, along with another 17 miles under National Park Service administration on the Grand Canyon-Parashant.

Nearly 1,650 more miles will remain open on the two monuments, along with more than 275 miles for administrative use only, he said.

Environmentalists fear the land will come under increasing pressure from thousands of tourists and off-highway vehicle enthusiasts in the next 20 years. The surrounding communities in Nevada and Utah are expected to grow by an estimated 1.4 million new residents in that time.